Busy-signal for telephone trunk-lines.



PATENTED OCT. 18, 1904.

P. R.-M0BBRTY. BUSY SIGNAL FOR TELEPHONE TRUNK LINES.

APPLICATION FILED JAN.14, 1901.

N0 MODEL. 7

, lhventor: Frank R.MSB EY.-

Attorney.

UNITED STATES Patented October 18, 1904.

PATENT OFFICE.

FRANK R. MoBERTY, EVANSTON, ILLINOIS, ASSIGNOR TO THE WESTERN ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

BUSY-SIGNAL FOR TELEPHONE TRUNK-LINES.

SPECIFICATION forming part of Letters Patent N0. 772,897, datedOctober 18,}904.

Application filed January 14, 1901- Serial No. 43,259. (No model.) 7

To all whom it may concern:

Be it knownthat I, FRANK R. MGBERTY, a

citizen of the United States, residing at Evanston, in the county of Cook and State of Illinois, have invented a certain newand useful Improvement in Busy-Signals for Telephone Trunk-Lines, of which the following is a full, clear, concise, and exact description.

This invention concerns means for testing lines in telephone-exchanges to determine whether they are free to receive connections. It is designed to give a busy-test indication, preferably a visible signal at one terminal sta' tion of a line when the required line is tested and found busy at the distant terminal of the line, as in the case of an interoffice trunkline, to signalize by a visible-indication to the answering or Aoperator'that a line called for is found already in use when tested at the receiving or B terminal of the trunk-line.

It is usual in the art of telephony for the B operator, having received a call for connection with a designated subscribers line terminating before her, and finding the line in use through a prior connection, to insert the terminal plug of the trunk-line through which the line of the calling subscriber has been temporarily extended to her station into a trunk-line to ascertain the presence of the busy indication, and upon the B operator the unnecessary work of removing the terminal plug of the trunk-line from the special busytone jack.

In devising my improvement I have aimed to avoid the acts of the A and Boperators mentioned; to cause the B operators test of the line called for to display before theA op- A erator a visible signal showing the busy condition of the line, permitting the B operator to replace the terminal plug of the trunk-line in its seat and dismiss the attempted connecsponsive to the test-current derived from a busy line, a visible signal at the other, the

originating terminal controlled by this instrument, means made active in the response of the instrument for maintaining the display of the signal after the cessation of the momentary testing-current, and other means controlled at the originating terminal for restoring the mechanism .to its initial condition in readiness for a test.

A suitable combination of my invention with the mechanism found in the prevailing switching system for telephone exchanges may be organized. as follows: An electromagnet capable of responding to the test-current distinctive of busy lines is connected in a ground branch from the testing-contact, usually the tip, of the terminal plug of the trunkline atthe B station. This magnet actuates relay-contacts, which in turn control a circuit through the trunk-line,which includes a visible signal, as a supervisory signal, at the A terminal of the line, a winding of the magnet beinginterpolated in the circuitso controlled; and a source of current being applied to the trunk-line at the A terminal of the trunk-line, so that the circuit when closed by the magnet maintains the excitement of the latter as Well as the display of the signal. An electromagnetic switch arranged at the B terminal to cut off the normal connections of the trunkline with this test-indicating magnet during the use of the line for conversation, its actuating-magnet being placed in a local circuit closed in registering contacts of the terminal plug and the spring-jack in which it is incontrolled by a suitable switch at the A terminal actuated in breaking the connection there with the trunk-line. If it is desired to utilize the supervisory signal associated with the calling-plug at the A station to indicate the busy test as above suggested, the special circuit applied by the testindicating magnet to the trunk-line is led through a constantlyoperating circuit-controller, which varies the resistance of the circuit to cause the signal to be intermittentlydisplayed in a characteristic manner without rendering the current ineffective for locking the magnet. I will describe this form of the invention more fully in connection with the drawing.

The diagram illustrates two substation-lines entering different central otfices, a trunk-line between the officcs with the usual associated appliances and the special mechanism of the invention connected with the trunk-line. The circuits and apparatus are well known to telephone-engineers as constituting the central battery system.

The lines from the substations (L and enter switchboards in the olfices A and B, respectively. Atrunk-line 1 E2 extendsbetween the oflices, ending in multipled spring-jacks in the switchboard at the A otlice and in a terminal plug at the B otfice. Pairs of plugs and their plug-circuits in the switchboard at the A oflice serve to unite any calling-line with the trunk-line leading to the B ol'tice, wherein the line called for can be reached. A central battery 0 for supplying current to excite the substation-transmitters and to operate the visible signals is connected in a bridge of the plug-circuit 3 4. In the path of current from this source to the called line a supervisory relay (Z is interposed, which controls by means of a shunt a supervisory signal 6 in a local battery-circuit 5 6, which becomes closed in registering contacts of plug f and the thimble of aspring-jackin which the plug is placed. In applying the invention to this system of circuits I provide an electromagnetic switch g, a test-indicating relay /L, and aconstantlyoperating circuit-controller The actuating-magnet of the switch ,r is connected in a conductor 7, terminating in the local contact of terminal plug of the trunk-line, through which it is united with the local conductor terminating in the testing of any substationline with which it is connected. The switchcontacts g g of the switch control a normal break in conductor 1 of the trunk-line. Switchcontacts 9 control acircuit 8 from the portion of conductor 1 leading to the testing-tip of plug 7", which traverses one of two windings upon the magnet of relay /L, a derivation of the circuit being taken through the telephone of the B operator also. The switchcontacts g g control a conductor 9, leading from conductor 2 of the trunk-line to earth through the circuitcontroller 2'. This path last traced also traverses the other winding l 7t of magnet 7t and is controlled by the re- 1 lay-contacts of that magnet.

The circuit-controller is permanently shunted by a coil Zot' high resistance, say ten thousand ohms, suliicient to preventthe operation of the supervisory relay (1 when thrown into its circuit. The controller operates to shortcircuit this resistance periodically, as twice in a second. The locking-wilnling should have suiiicient power to hold the armature of relay ll. even when the coil is in the circuit.

In the operation of the system here presented incoming calls reach the A oilice and are answered by the A operator. who may give the order for the line called tor to the proper B operator over an order-wire. The B operator designates a trunk-line l 2 to be used in making up the connection, and the A operator immediately links the calling-line with the trunk-line by inserting the ma to plug of the one used for answering the call into the spring-jack of the trunk-line. The B operator tests the line called for by applying the tip of the plug Z' to the test-ring of its termi nal spring-jack. It the line is in use or busy, a test-current is derived through the test-tip. which flowing to earth through conductor H excites testindicatingmagnet 7t and draws up its armature. The closu re of the contacts of this relay completes a circuit from the central battery at the A terminal ot the trunleline through one conductor 2 of the trunk-line and wire 9, which maintains the magnetization of the relay 71. and brings the supervism'y relay (1 under the control of the circuit-controller The relay (Z when excited closes the shuntabout the supervisory lamp c, which. it will be noted, was lighted by current in the in the terminal jack of the trunk-line; but through the action of .the controller 1' at the B otlice its excitement is made intermittent, and the lamp is caused to give a. pulsating or flickering signal which, being characteristic, constitutes the visible busy-signal. The B operator at the same time hears the click pro duced in her telephone by the derived testcurrent and replaces the plug X in its seat. The A operator may notify the calling party of the failure to secure the called lini and will then remove the plngf from the trunkjack. Severing the connection of battery 0 from the trunk-line deprives the lockingwinding it of current and returns the mechanism to its initial position. When the B operator linds the line tested tree for the desired connection, she places the plug Z in the jack of the line wanted. This insertion of the plug closes the local circuit 7 (5, including the magnet g, which, being excited, breaks the connection of branches 8 and 9 with the trunk-line and closes the break in the conductor 1, completing the desired electrical circuit between the substations.

The B operator may disconnect the trunklocal circuit completed by placing the plugj" line from the line called for upon observing the clearing-out signal of the supervisory lamp or she may be furnished with a special disconnection signal controlled by any of the well-known devices.

My invention may be modified or embodied ling the same, a test-indicating magnet responsive to changes in the electrical condition of said circuit, a busy-signal indicator controlled by the magnet, and a locking device made active in the response of the magnet for maintaining the busy indication after the cessation of the test-current through the for changing the electrical condition of the magnet, as described.

2. The combination with telephone-lines, test-contacts associated therewith and means test-contacts of a line in making connection with the line, of a testing-contact, a magnet responsive to the test-current derived from the test-contacts, a busy-test signal-indicating device controlled by the magnet, a looking device for maintaining the indication thereof after the cessation of the testing-current, and means for rendering the locking devlce ineffective, as described,

3. Thecombination with a telephone-line, test-contacts associated therewith, 'atest-circuit of the line adapted for closure at one point in making connection with the line and at another point through a testing-tip of a terminal plug of a telephone trunk-line, of a test-indicating magnet responsive to the testing-current connected with the tip, a busytest-indicating device at the distant terminal of the trunk-line in a circuit controlled by the magnet, a locking-circuit made effective in the, response of the magnet adapted to maintain the signal independent of the busy-test current, and a switch at the said distant terminal forbreaking the locking-circuit, as described.

4. The combination with telephone lines and test-circuits and test-contacts thereof, a link conductor, as a trunk-line, and means for connecting a telephone-line therewith at either end, of a testing-tip forming a terminal of j the link conductor, a magnet responsive to I testing-current, connected with said testingtrp, a test-indicatlng instrument associated with said tip and adapted to indicate a testcurrent, another test-signal-indicating device at the distant station in a circuit controlled by said magnet, a locking device actuated by said magnet adapted to maintain the closure of circuit controlled thereby after the cessa tion of testing-current, and a switch actuated in breaking connection with said-link conductor at .the distant station controlling the locking device to render it inelfective, as described.

'5. The combination with telephone-linescentered at answering and receiving switchboards and test-circuits for said lines, of a trunk-line extending between the switchboards having a plug-terminal at the receiving end, a testindicating magnet responsive to testing-current connected with said plug and a testing-telephone also connected therewith at the receiving-switchboard, avisible signal at'the answering-switchboard and a circuit therefor controlled by said magnet, a' locking-circuit for the magnet'controlled by the magnet, aswitch at the answering-switchboard for breaking the locking-circuit, and an electromagnetic switch at the receivmgswitchboard having itsmagnet in a local circuit closed by the terminal plug of the trunkline in making connection with another line at the receiving-switchboard, said switch be ing adapted to breakthe normal circuits from FRANK R. MOBERTY.

' WVitnesses:

ELLA EDLER, ADELL HooKE'rr. 

